This is really a trig question.  I have been using atn(1/6) for our standard tapered ball joint angles.  All derivations and definitions of the function say it should give me the angle.  It's close, but when I force a 1:6 ratio angle it results in an angle of 9.527283˚.  atn(1/6) yields 9.462322˚  Can anyone explain why there is a difference?  Using a calculator yields the same thing as SW.  The difference is enough for our tapers not to seat correctly.